Conventional automatic vehicles may include a transmission having a torque converter to provide a hydrodynamic coupling with torque multiplication. The hydrodynamic coupling allows the engine to continue running while connected to the transmission when the vehicle is stationary. In addition, the torque converter provides torque multiplication to assist vehicle launch and provides damping of driveline torque disturbances. The torque multiplication or torque ratio varies with the speed difference or slip between the torque converter input element (impeller) and output element (turbine). A torque converter clutch or bypass clutch may be provided to mechanically or frictionally couple the impeller and the turbine to eliminate the slip and associated losses to improve efficiency. The bypass clutch has an associated clutch capacity indicating a maximum torque transferrable by the torque converter without slipping.
Similarly, hybrid vehicle powertrains may include a transmission or gearbox having a torque converter arranged downstream of an electric machine, i.e. between the electric machine and vehicle wheels. The electric machine may be configured to provide either drive torque, which may conventionally be referred to as positive torque, or regenerative braking torque, which may be referred to as negative torque.